LAGOS, Nigeria – LAGOS, Nigeria (AP) — Royal Dutch Shell PLC said Thursday that a fire struck one of its major crude oil pipelines running through Nigeria's southern delta, cutting into production.

Meanwhile, Italian oil company Eni SpA said Thursday it had resumed daily production of 12,000 barrels of oil at one of its facilities in Nigeria's restive Niger Delta.

Shell is investigating what caused the fire on its Trans Niger pipeline, company spokesman Tony Okonedo said. Okonedo declined to say how badly the fire affected production.

"Teams have been mobilized to address the fire and the spill," the spokesman said.

The pipeline runs through the eastern part of the Niger Delta, a maze of creeks and swamps running through 20,000 square miles (nearly 52,00 square. kilometers) of southern Nigeria. The part of the pipeline affected sits in Ogoniland, an area Shell withdrew from in 1993 while it was under attack from activists who were sabotaging the oil wells and beating Shell staffers to get them to leave the region.

Shell's Nigerian subsidiary faces regular attacks by militants who have targeted pipelines, kidnapped petroleum company workers and fought government troops since 2006. Shell's chief executive officer has even hinted that the company can no longer depend on Nigeria as a profit-maker, despite its 50-year history in the country.

Such production disruptions in Nigeria have affected global oil prices in the past. Nigeria was the No. 4 oil exporter to the U.S. in February, sending about 896,000 barrels of crude a day to the U.S., outstripping even Saudi Arabia.

Meanwhile, an Eni spokesman told The Associated Press on Thursday that the company had resumed production Wednesday at its subsidiary's Brass River oil operation after declaring an end to a force majeure — a disruption ordered when an oil producer cannot meet promised supply.

The spokesperson did not say what prompted Wednesday's action. The facility is in an area often beset by militant attacks. The spokesperson spoke on condition of anonymity in line with company policy.

The company most recently declared a force majeure at the facility in late April but did not give details.